1. Field of the Invention
The present invention relates to a driving circuit of multi-lamps and more particularly, to a driving circuit that can detect whether the multi-lamps are in abnormal states and thereby activate a protection mechanism.
2. Description of Related Art
The liquid crystal display (LCD) has become a mainstream in the market due to its advantages of low power consumption, no radiation, and low electromagnetic interference. Generally, the LCD includes an LCD panel and a backlight module. Since the LCD panel has no capacity of emitting light by itself, the backlight module is disposed for providing a light source required by the LCD panel. The backlight module is generally implemented by a cold cathode fluorescent lamp (CCFL) to serve as a light source.
As design of the LCD panel has a development trend toward vast size, application of multi-lamps is inevitable. However, utilization of the multi-lamps can cause a number of problems, for example, brightness inconsistency caused by uneven distribution of a lamp current, management of abnormal states such as a short circuit or an open circuit occurring in the lamps, and design of a protection circuit aimed at protecting human safety.
FIG. 1 is a schematic diagram illustrating a conventional protection circuit of multi-lamps. Referring to FIG. 1, current detection devices 120a and 120b respectively detect currents of lamps 110a and 110b to determine whether the lamps 110a and 110b are in the abnormal states. When the lamps 110a and 110b are under normal operation, signals at nodes Xa and Xb are at a high level. If one of the lamps (e.g. the lamp 110a) malfunctions or has a problem of short circuit or open circuit, the level of the signal at the node Xa then decreases to near zero. In the meanwhile, a diode Da within the current detection device 120a is conducted to activate a protection circuit 130 so as to prevent transformers 140a and 140b from outputting voltages to the lamps 110a and 110b. 
Certainly, a plurality of voltage detection devices can be applied to respectively detect the voltage levels of the lamps in the protection circuit of the multi-lamps so as to detect an operation state of each lamp and accordingly determine whether or not to activate the protection circuit 130. However, the conventional protection circuit of the multi-lamps adopting a method of independently detecting the operation state of each lamp. Namely, the quantity of the current or voltage detection devices increases with the quantity of lamps, which indeed leads to additional hardware cost.